The wireless coverage indoors of a mobile communication system is not so high. There are several reasons. For example, wireless electric waves are difficult to reach the inside of a building and it costs much to set and administer an indoor-type wireless base station.
Under this situation, a microminiature wireless base station (BTS: Base Transceiver Station) called “Femtocell” has been proposed recently. This BTS is assumed to be used inside a house or an office and it conforms to, for example, the Wideband-Code Division Multiple Access (W-CDMA) method, enabling a simultaneous communication for a small number of users (about four users) by forming a small sized cell (femtocell) having a radius of several tens meters. Further, the cost is low.
In order to improve the indoor coverage without raising the management cost, it is conceived that this microminiature BTS (hereinafter, referred to as a femtocell BTS) is arranged inside a tall building or an underground facility (dead zone) that could not be covered by the existing wireless base station.
Further, a technique of remotely setting an Radio Frequency (RF) unit connected with an existing base station via a cable line to the base station, is known as a means for improving the coverage of the mobile communication system.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-40802    [Patent Document 2] Japanese Patent Application National Publication (Laid-Open) No. 2002-524989    [Non Patent Document 1] “A follow up article on 3GSM Korea Samsung and NEC exhibit “Femtocell”    [Non Patent Document 2] “Manufacturing Agreement For Zone Gate Low-Cost Residential 3G Access Point”.    [Non Patent Document 3] NTT DoCoMo Technical Journal Vol. 15 No. 1, [online], April, 2007.
Since the femtocell BTS is supposed to be set indoors, the number of the femtocell BTSs being set is expected large. However, there is a limit to the capacity (for example, several hundreds BTSs) in a device that accommodates the base stations and controls them (RNC: Radio Network Controller). Therefore, it cannot help but increase the number of large-sized expensive RNCs, in order to accommodate a large number of femtocell BTSs (for example, more than several thousands BTSs).